1. Field of the Invention
The present invention relates to an optical recording medium such as DVD, and particularly relates to an optical recording medium in which recording tracks are formed meanderingly.
2. Description of the Related Art
In recent years, DVD is used as an optical information recording medium with large capacity generally and widely. In addition to Read-only DVD (DVD-ROM), the standard of DVD-RW (DVD-Re-recordable) being capable of recording and reproducing recording information is being laid down. Groove tracks are formed as recording tracks in a predetermined pattern on an optical disc according to the DVD-RW standard. The groove tracks are formed meanderingly so as to be wobbled, and a wobble signal with constant frequency is extracted at the time of recording so as to be capable of being used as a reference signal which synchronizes with rotation of the DVD-RW.
Meanwhile, since recording is possible on DVD-RW, for example, various contents data recorded on DVD-ROM can be illegally copied onto DVD-RW. Contents such as images and music are normally subject to protection of their copyright, and it is requested that illegal copying onto DVD-RW is prevented by a certain method and the copyright is protected effectively.
Therefore, in the standard of DVD-RW (Ver.1.0), measures for preventing illegal copying is defined, namely, predetermined data are previously embedded as emboss pit string (phase pit string) into an area of DVD-RW corresponding to a recording area of DVD-ROM where reproduction control data or the like were recorded. As a result, even if other reproduction control data are overwritten on this area, a reproduction signal of the overwritten data interferes with the reproduction signal of the emboss pit string so as not to be read, and thus other reproduction control data cannot be substantially overwritten.
However, since the area into which the emboss pit string was embedded is equal to that grooves are formed intermittently, an output level of a wobble signal extracted from this area is lower than an output level of a wobble signal extracted from an area of a continuous groove where recording data are recorded, and thus synchronous detection of DVD-RW cannot be executed stably.